Kotlin - expected: java.util.Collections$SingletonList but was: java.util.ArrayList. Why?

Question

Kotlin

I apologize in advance for the stupid question. I googled, didn't find anything specific on the Singleton topic.
org.opentest4j.AssertionFailedError: expected: [email protected]<[line]> but was: [email protected]<[line]>
The compilation result is correct, it gives me the desired list, the tests match the result . The only thing is that it complains about waiting for a Singleton, while fun text(text: String): Any. Why? Where can I read what exactly is the Singleton type and the most common questions about it?

Answer 1

In short, apparently, you have a test where you do something like assertEquals(<что-то>, text(<что-то-ещё>));
Lists you get in different ways. mutableListOf returns a java.util.ArrayList, and a SingletonList is obtained from a single element by calling Collections.singletonList(something). equals is apparently not overridden there (I don’t remember now), which is why it turns out such garbage.